Planning of economical load distribution has been conducted to keep the total power generation cost including such as fuel and start-up expenses at minimum, or maximizing the selling price of generated power while satisfying the demand for power using various mathematical programming. For example, NPL 1 discloses a technology of planning power demand and power supply so that the 24-hour power generation cost is kept at minimum. And PTL 1 discloses a technology of planning the water level of a reservoir so that the price of generated power is maximized. Further, there is a case where the power price for the next day is presented to a customer for the customer to check and determine the amount of electric power demand to use. For example, PTL 2 discloses a technology of controlling the temperature of hot water in a calorifier type tank so that the electric power cost for heating is minimized. In recent years, experiments are being performed to control the demand with real-time power prices which is called a smart grid.